Nor does C4 contribute to the operation of the circuit because of the high resistance of VR2, and C1 is effectively shorted out by the wiper of VR1 being at the top end of its resistance track. 4.2.3.īoth bass and treble potentiometers that may have either linear or logarithmic tracks depending on the circuit design, are much higher values than other components in the circuit, and so with the VR1 and VR2 wipers set to maximum resistance both potentiometers can be considered to be open circuit. With bass and treble controls set to maximum boost (both wipers at the top of resistors VR1 and VR2), and the inactive components greyed out, the circuit will look like Fig. Baxandall B.Sc.(Eng.) published in "Wireless World" (Now Electronics World) How the Baxandall Circuit Works. Read the original 1952 paper "Negative-Feedback Tone Control" by P. In passive variants of the Baxandall circuit, extra stages of amplification may be used to make up for the approximately −20bB attenuation caused by the circuit. There are still many variants of the circuit in use, both as active circuits (with amplification as originally proposed), and as passive networks without an incorporated amplifier. Baxandall in 1952, used a valve (tube) amplifier and feedback as part of the circuit to reduce the considerable attenuation ( about −20dB) introduced by the passive network, and to provide true bass and treble boost. 4.2.2, which is an analogue circuit providing independent control of bass and treble frequencies both bass and treble can be boosted or cut and with both controls at their mid positions, provides a relatively flat frequency response, as illustrated by the blue ‘Level response’ graph line in Fig. The circuit discussed here is an example of the Baxandall tone control circuit, illustrated in Fig. These range from simple RC filters, through passive and active frequency control networks to complex digital signal processing. many techniques are used to alter the sound, and in particular the frequency response of the amplifiers producing the sound. The room or hall in which the sound is reproduced will also affect the nature of the sound. This may be done to suit the preferences of the listener, not everyone perceives sound in exactly the same way, for example the frequency response of the human ear changes with age. In hi-fi amplifiers, tone control refers to the boosting or reduction of particular audio frequencies. The use of these simple circuits is normally restricted to guitar applications or inexpensive radios. As the circuit only reduces the high frequency content of the signal it could be called a simple Treble Cut control. a simple method of achieving this is to place a variable CR network between the voltage amplifier and the power amplifier stages, The value of C1 is chosen to pass the higher audio frequencies, this has the effect of progressively reducing the higher frequencies as the variable resistor slider is adjusted towards the bottom end of the tone control, The minimum level of attenuation of the higher (treble) frequencies is limited by R1, which prevents C1 being connected directly to ground. 4.2.1 provides a simple means of regulating the amount of higher frequencies present in the output signal fed to the loudspeakers. Tone Control, shown in its most basic form in Fig.
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